Change in the activity of excitable membranes is a cornerstone of functional modification within the vertebrate nervous system. Modification of nervous system activity, in turn, is a cornerstone of behavioral change in vertebrates. Thus, understanding the regulation of excitable membranes contributes to our understanding of nervous system function and relating these changes to in vivo behavioral changes presents a powerful approach to an integrated understanding of behavior change and its biological bases. An ideal model for such research is the weakly electric fish, B. pinnicaudatus, which generates electric fields, known as electric organ discharges (EODs), for electrolocation and communication. The amplitude and duration of the EOD waveform varies in response to environmental variables apparently controlled by steroid effects. Because the EOD results from synchronized ionic membrane currents of all electrocytes within the electric organ, changes in EOD waveform reflect changes in ion currents of individual electrocytes. By determining the cellular and molecular mechanisms of EOD waveform change it is possible to determine a chain of continuous causal connections relating environmentally controlled behavior to its neural, endocrine, and cellular causes. The project proposed here will apply electrophysiological techniques including single unit recording, two-electrode voltage clamp, and patch-clamp recording to discover the physiological mechanisms by which B. pinnicaudatus regulate these changes inEOD. The project's specific aims are to 1) relate the phases of the EOD to its corresponding extracellular potentials and intracellular action potentials 2) determine which ion currents contribute to the two phases of the extracellular potential and to the intracellular action potential 3) determine the mechanisms by which rapid changes in EOD waveform are expressed in the extracellular potentials and intracellular potentials and intracellular potentials of individual electrocytes, and 4) determine how specific ion currents change when the EOD changes in amplitude and duration.